Identification of differentially expressed genes under drought stress in perennial ryegrass

Perennial ryegrass (Lolium perenne L.) is a widely used cool-season forage and turf grass species. Drought stress can significantly affect the growth and development of grass plants. Identification of genes involved in drought tolerance facilitates genetic improvement of perennial ryegrass. A forward and a reverse cDNA library were constructed in drought-tolerant (PI 440474) and drought-susceptible (PI 204085) accessions by using suppression subtractive hybridization (SSH). A BLAST search revealed that 95 of 256 expressed sequence tags (ESTs) obtained from the two libraries showed significant sequence homologies to genes with known functions. They were classified into different putative functional groups including amino acid metabolism, lipid metabolism, carbohydrate metabolism, transcription, protein synthesis and destination, energy, photosynthesis, signal transduction, cellular transport and detoxification. Among them, 50 ESTs were from forward library (the drought tolerant over the susceptible accession). The expression patterns (reverse transcriptase polymerase chain reaction) of the selected genes encoding mitogen-activated protein kinase, superoxide dismutase and glutathione peroxidase (GPX) in additional accessions contrasting in drought tolerance were generally consistent with patterns of differentially expressed genes identified through SSH. The GPX fragment had a high degree of nucleotide diversity (pi = 0.0251) in the selected perennial ryegrass accessions. The results suggest that differentially expressed genes between drought tolerant and susceptible accessions may play an important role in the drought tolerance of perennial ryegrass. They can be used as candidate genes in examining nucleotide polymorphisms and conducting the association analysis of genes with drought tolerance.